TGFbeta mRNAs for all three mammalian isoforms are variably expressed by human mammary epithelial cells. The reported effects of TGFbeta on angiogenesis, stroma formation, and host immune surveillance suggest its involvement in tumor progression. In addition, highly tumorigenic hormone-independent, estrogen receptor (ER)-negative human breast cancer cell lines secrete higher levels of TGFbeta activity (protein) and exhibit higher levels of TGFbeta receptors than hormone-dependent, ER-positive cell lines. We have recently reported that transfection into and overexpression of TGFbeta1 by estrogen-dependent MCF-7 breast cancer cells allow them to bypass hormone dependence in athymic mice. Moreover, neutralizing anti-TGFbeta antibodies inhibit tumor formation by MDA-231 human breast cancer cells in athymic mice. In this project we will systematically study the role of the TGFbeta system in the biology of human breast epithelial cells. Several approaches will be taken to address these questions. First, a systematic analysis of TGF-beta1, - beta2, and -beta3, and type II and III TGFbeta receptor expression in a defined spectrum of breast lesions (hyperplastic, dysplastic, and noninvasive and invasive carcinomas) as well as normal and tumorigenic cultured mammary cell lines. Northern blot analysis, nucleic acid in situ hybridization, immunohistochemistry, affinity crosslinking to 125/I- TGFbeta, 35/S-labeling plus immunoprecipitation, and immunoblotting will be used. Second, type II TGFbeta receptors will be transfected and overexpressed in normal and breast tumor lines followed by an assessment of this transfection on in vitro transformation, on tumorigenicity in nude mice, and on antiestrogen sensitivity or resistance. Third, the impact of exogenous TGF-beta1 and anti-TGFbeta neutralizing antibodies on the progression of preneoplastic and neoplastic mouse mammary cells in Balb/C mice will be examined. Fourth, we will test the effect of TGFbeta blockade on tamoxifen-mediated growth inhibition of hormone-dependent breast carcinoma cells in vitro and in nude mice and on antiestrogen- resistant cell lines and xenografts. TGFbeta blockade will be done with anti-TGFbeta monoclonal antibodies or by transfection of dominant negative type I and II TGFbeta receptor expression plasmids.